SOPRASEAL LM 203 is a one-component spray applied non-permeable air barrier membrane used in wall construction. SOPRASEAL LM 203 is a water-based, ultra low VOC liquid product composed of a modified rubber formulation for elongation. This non-flammable, non-permeable air barrier provides moisture protection behind wall claddings such as brick, siding, metal panels, EIFS and stucco. Utilization of a slipsheet is required for stucco cladding.

Product Properties

  • Air Permeability ASTM ASTM E2178
  • Air Permeability ASTM ASTM E2357
  • Air Permeability ASTM ASTM E283


To apply SOPRASEAL LM 203 mix the product until thoroughly blended. To apply SOPRASEAL LM 203 at temperatures below 40°F (4°C) but above 25°F (-4°C), blend with one quart container of SOPRASEAL LT Additive. Use a ¾” (19 mm) nap roller, paint brush or spray equipment to apply. Please refer to SOPREMA specifications and installation instructions for additional application guidelines prior to use.


Testing & Approvals

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Related Projects

Garibaldi Square Condos – Chicago, Illinois

This award winning project is the direct result of the building owner’s resistance to using hot asphalt and torches on the roof. SOPREMA’s mechanically attached, self-adhered system was used to accommodate the building owner’s desires.

Airport High School – West Columbia, South Carolina

Because of the uneven surface of the remaining embedded aggregate, SOPRAROCK® was chosen knowing that this board would conform to the uneven surface much better than a rigid coverboard could. This idea spawned another....”why not use SOPRASMART® XP”; and allow one application step instead of two. The project was capped off with SOPRALENE® 180 FR GR, in COLPLY® Adhesive.